Yet another weight question

I am very confused!
Will I be overweighted with a HP100.. or would a LP95 be a better choice? Should I switch to a plastic or alum backplate??



5'9" 125 lbs.. very low body fat (~3.0%)
30# wing w/ dive rite SS backplate/ hog harness
reg
13cf alum pony with reg
3/2 full wetsuit
7mm booties
Warm salt water diving (S. FL)
wrist comp/compass/knife

Seems like this has been discussed, recently...

An LP tank will never be a better choice than a HP UNLESS you plan to overfill it. I don't believe in overfilling so I'll skip that part.

There is a 'sticky' spreadsheet over in the Equipment -> BCs forum that shows you how much weight and how much lift you need at each of the 4 phases of a dive: floating at the surface before descent, at depth when the wetsuit is compressed and the tank is full, at depth when the wetsuit is compressed and the tank is empty and, finally, at the surface when the tank is empty.

To use it, you need to know how much weight it takes to sink your wetsuit. Then you have to guess how much buoyancy it loses at depth. It can't be much because it doesn't have a lot to lose. Then you can try various rig weights (aluminum vs stainless backplates) and tank buoyancies.

I am not a fan of steel tanks for warm water (T shirt) diving. You are always negative and you don't have ANY ditchable weight. For that reason, I prefer the old aluminum 80. Almost nobody agrees with me. They are entirely comfortable diving in a rig that will not allow the diver to be made positive by ditching the weight belt. And ditching weights is the very first step of rescue when you get a diver to the surface. But I digress...

With a 3mm wetsuit, you MIGHT need 10# of ballast to sink the suit. I don't know the right number. You suit is much smaller than mine (I weigh north of 210) and mine is 7/8mm, Your suit might give up 5# of buoyancy at depth.

Then, you need need +10# - 2.5# (buoyancy of empty HP 100) or 7.5# of ballast. Actually, the reg will be a couple of # so you need about 5#. With this configuration, you can float on the surface with an EMPTY tank by ditching your weight even if the wing is blown. You will be a couple of # negative on the surface with a full tank and a blown wing even dumping your weight.

What I haven't factored in is the weight of the backplate and it can only work to make you more negative. I suspect I would opt for Kydex over aluminum and I certainly wouldn't consider stainless steel.

Maximum wing lift is required when the HP 100 is full (-10.5#) and the wetsuit has been compressed to +5# and you still have a -2# regulator and -5# of lead. Something like 13# of lift is about right. You certainly don't want 30# of lift. The wing will have a larger profile and require more effort to drag through the water.

You really need to call Tobin at Deep Sea Supply. He is the expert on getting the right setup.

Richard

A wing with 30 lbs. of lift is more than enough for your configuration: HP100/LP95 + SS BP + 3mm wetsuit. A wing with 20 lbs. of lift would probably be sufficient.
Get a HP100 or LP95 or AL80. There isn't a bad choice among them really. Depending on the model of LP95, it will be a few pounds heavier topside than the HP100. Check this online chart to see to compare tank buoyancy specs. Once in the water, the buoyancy characteristics are quite similar. It's nice having a little extra gas for certain dive sites, though, so that might lead you away from the AL80.

If you insist on having some ditchable weight, you may want to go for the Kydex (Deep Sea Supply only) or AL BP. You should know, however, that an AL BP is only about 4 lbs. lighter than a SS BP. That being said, many people dive a SS BP + no additional lead with thin exposure protection (warm water) and are very happy with it.

When diving AL80 tanks, my warm water setup is an AL BP + 4 lbs. on tank cambands + 3 mm wetsuit. I use my 30 lb. lift wing because I'm a cold water diver who's too cheap to buy a smaller wing. It works just fine. I could have made the 4 lbs. ditchable, but if I put the 4 lbs. on my hips it makes me annoyingly foot heavy (poor trim = bad). Essentially, I have no ditchable weight, and I'm OK with that. Bringing my SS BP on vacation would work, but I'd rather save that 4 lbs. in my luggage for souvenirs.

LP95s and HP100s trim out nicely for me. Since you're 5'9", I suspect they'd work for you, too. I have one Worthington X7-HP100 and one PST HP100. They're both great. I hear Florida cave divers like to get LP tanks and overfill them (past the rated service pressure) for more capacity. If cave diving is in your future, you might want to consider that. rstofer gives good advice about AL80s. I have a couple of those, and they work just fine.

Once you really get into diving, you'll start collecting tanks like pairs of shoes. It's a convenience thing. The more tanks you have, the fewer trips you have to make to the dive shop to get fills. Pretty soon you'll be trying to figure out where to store all of them.

Have fun with your gear purchases...

I doubt you will have any ditchable weight, and likely will be a few pounds negative even on an empty tank. That is not necessary bad, but in the event of a wing failure you still need to be able to swim your rig to the surface at it's most negative (full tank and deep with a fully compressed wetsuit).

I would likely go with an aluminum, or kydex backplate in your situation and try to get a few pounds of ditchable weight.

scubasteve0011:

I am very confused!
Will I be overweighted with a HP100.. or would a LP95 be a better choice? Should I switch to a plastic or alum backplate??



5'9" 125 lbs.. very low body fat (~3.0%)
30# wing w/ dive rite SS backplate/ hog harness
reg
13cf alum pony with reg
3/2 full wetsuit
7mm booties
Warm salt water diving (S. FL)
wrist comp/compass/knife

Click to expand...

You would be negative even with a neutral BP. I'm 6'3 and 200lb, fit(although I haven't hit the gym in 3 months and have been eating like crap), but definately higher than 3% body fat. I only need 1 lb with BCD wihout wetsuit and 3lb with my 3mil using a Worthington HP100 or a PST HP100 (which means I'm probably still a pound overweighted with the Worthington).

Mr Carcharodon:

I doubt you will have any ditchable weight, and likely will be a few pounds negative even on an empty tank. That is not necessary bad, but in the event of a wing failure you still need to be able to swim your rig to the surface at it's most negative (full tank and deep with a fully compressed wetsuit).

I would likely go with an aluminum, or kydex backplate in your situation and try to get a few pounds of ditchable weight.

Click to expand...

The reason I keep preaching ditchable weight is because the first task upon getting a victim to the surface is to make them positive. Sure, the wing may work fine. Or not... But what I was trained to do is ditch the weight.

Now, if all the weight is permanently integrated and I can't ditch it then the wing better work and I had better understand the mechanism. If it doesn't I am struggling with the victim while trying to figure out why they don't float. Finally, I ditch their rig.

All of a sudden I have lost the capability of using a 'tank tow' and the victim can't breathe off their own tank because it is at the bottom of the ocean. I have to provide air while I do a side tow. If I have a long hose primary for the victim then I might be able to do a 'fin push'.

I have lost a lot of flexibility as a rescuer because the rig was never properly balanced. And don't make the assumption that I am rescuing my buddy and therefore know all about the equipment. It doesn't always work out that way.

I'm getting old and I spend too much time thinking about rescue. In my view, warm water divers should not be using tanks that are very negative. The aluminum 80 is perfect for warm water. I haven't checked the characteristics of an aluminum 100 but that might be an option.

Again, not many agree with me.

Richard

A steel tank adds about 5~6lbs to the setup, IOW's take that off your belt. If you don't have that weight to take off the belt, than YES, you will be over-weighted especially at the start of the dive.

You did not say how much weight you use currently.

Ways to fix that are a lighter BP, or loose some muscle!

You could also add a little buoyancy to your tanks. A little bit of Styrofoam would do it.

RonFrank:

Ways to fix that are a lighter BP, or loose some muscle!

Click to expand...

At 5'9 and what I think he meant to type 152 he can't be loosing anything! If he's really 125 (which I assume is a typo) he really has nothing to loose and probably needs a smaller, lighter and neutrally bouyant tank.

He indicates he is diving with a Steel BP. If that is the case, he can switch to Alum or Kydex and loose most of the weight there if necessary. Plates are relatively inexpensive.